1. Field of the Invention
This invention relates to a photosensitive recording medium used in image-forming apparatus.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 5-39303 discloses a conventional photosensitive recording medium coated with photosensitive microcapsules so that color images can be transferred and formed on plain paper.
This photosensitive recording medium comprises a base material such as paper or resin film and a photosensitive layer coated on the base material, and the photosensitive layer is further coated with photosensitive microcapsules having as materials encapsulated therein a photosensitive material capable of hardening upon reaction with light and an image-forming material comprising a pigment or the like.
Thus, upon exposure of this photosensitive recording medium to light in accordance with image information, there occur some areas in which the photosensitive microcapsules have hardened and other areas in which they have not hardened. Thereafter, this medium and plain paper are brought into face-to-face contact, which are then, e.g., passed through a pair of pressure rollers so that an external force is applied to the microcapsules, whereupon the microcapsules having not hardened are collapsed but the microcapsules having hardened are not collapsed. From the microcapsules thus collapsed, the encapsulated materials comprising the image-forming material are released. Then, upon transfer of the encapsulated materials to the plain paper, images are formed on the plain paper.
However, the photosensitive recording medium disclosed in this publication employs photosensitive microcapsules which are sensitive to light with a wavelength of the ultraviolet region, and hence, for writing, the medium must be exposed to ultraviolet light before images are recorded, resulting in a very low practical utility. In particular, it has been impossible to reproduce any existing color images on plain paper by using the medium.
Accordingly, the present applicants have made studies to bring out a visible-light photosensitive material capable of directly hardening upon exposure to visible light rays. As the outcome of such studies, Japanese Patent Application Laid-open No. 3-39747 discloses a photo-hardening, photosensitive composition of such a material, and Japanese Patent Application Laid-open No. 3-77952 discloses a transfer recording medium employing such a photosensitive composition in the form of microcapsules.
Japanese Patent Applications Laid-open No. 6-27626, No. 6-51501 and No. 6-51502 also disclose image-forming microcapsules in which the above visible-light photosensitive material and an image-forming material such as a pigment are encapsulated.
In a disperse system in which such image-forming microcapsules are dispersed, a binder resin is added to prepare a coating composition, and this coating composition is coated on a base material such as plastic film so as to be in a stated thickness, followed by drying to form a coat layer. Thus, a photosensitive recording medium is obtained.
However, even with use of such a photosensitive recording medium, there have been problems such that images formed are unclear in some cases.
Stated specifically, images may have a low density, may have a whitish tone or have a blackish tone on the contrary, or may have an unnatural color tone in the case of color images.
Such problems are considered due to the fact that photosensitive recording mediums have differences in the quantity of colorants contained in the photosensitive layer of the photosensitive recording medium described above. The photosensitive recording medium is produced in the manner as described above, where the thickness of the photosensitive layer is fairly precisely controlled but it is difficult in manufacture to strictly control the quantity of the microcapsules contained in the photosensitive layer and the quantity of colorants contained in the microcapsules. As the result, individual photosensitive recording mediums have delicate differences in these.
In the case when the colorants are contained in the photosensitive layer in a relatively large quantity, the colorants that can be transferred to an image-receiving sheet are in a large quantity, resulting in a high image density as a matter of course. In such a case, however, the greater part of the amount of light used in exposure is absorbed by the colorants present in a large quantity, so that the light reaching the photosensitive material may become short. Hence, the microcapsules that should become hardened do not harden, and colorants having colors that should not be transferred are transferred, resulting in a poor color tone of the images formed.
On the other hand, in the case when the colorants are contained in the photosensitive layer in a small quantity, the light absorbed by the colorants is in a small amount, and hence the photosensitive material can better harden. Since, however, the colorants are in a small quantity, the image density may of course become low on the whole.
Thus, when an image-forming apparatus is designed to have a constant amount of light for exposure, the images formed may become different depending on the photosensitive recording mediums used.